For many years, double action or "toggle" presses were the industry standard for forming large metal parts such as automobile hoods. A toggle press has an outer ram that comes down and binds the blank to be formed. An inner ram with a punch having the desired part shape then follows through to draw the blank into a complementary shaped die cavity. In the quest for speed and efficiency, much of the industry is now using straightside or transfer presses which is the forming press to form the initial shape from the flat metal blank. Next, the part passes through a series of individual stations or presses to complete the necessary die operations, all in one combination process. Unfortunately, toggle presses are relatively slow and form the part in an inverted or upside down orientation. In most cases then, the toggle press will most likely have to include a turnover station following the draw operation. A solution to the speed and inversion problem is the use of the straightside press. Unlike the toggle press, where the outer ram comes down gently to bind the blank for drawing. Straightside presses have but a single ram with an upper die or binder that is actuated by the throw of the press crank cycling at up to 30 strokes per minute and at up to 30 inch strokes. The die cushion or lower binder surrounds a lower punch which defines the complementary part shape to the cavity of the upper die. The cushion floats around the punch and is supported in an up position upon a series of gas springs that collectively offer adequate force to bind the blank for the draw operation. When the upper die binder face meets the floating cushion and blank, the blank is instantly contained between the upper and lower binder faces. The impact between the ram and cushion at this instant is tremendous and is the result of the fast moving ram contacting the stationary cushion. The shock caused by this impact causes great damage to the press drive and creates undesirable pressure spikes in the individual cushion unit seals. After contact, because the ram force exceeds the resistance force of the gas cylinders, the ram, blank and cushion continue downward at the automatic press cycle speed until the they reach the bottom of the stroke, at which point the blank has been formed to the desired shape. At this point, the cushion cylinders have been compressed, and their resistive force has increased in accordance with the compression ratio of the nitrogen gas (Boyle's law). Cushion forces for major automotive dies commonly operate in the range of 200 to 300 tons. When the press ram reaches bottom position and starts its upstroke, the nitrogen gas cushion springs with their intensified pressure forces against the upper die throughout the die cushion upstroke. These forces cause major press drive damage, and stamping facilities have long been seeking a method to unload the cushion forces at the bottom of the press stroke so the cushion forces do not follow through causing such damage. Thus, while gains have been made in speed and efficiency form the use of straightside presses versus toggle presses, the wear and tear inherent in the application of straightside presses continues to plague its users.
What is needed is a way to abate or eliminate the wear and tear resulting from the high impact and recoil effect inherent in straightside presses using nitrogen spring-loaded die cushions and to delay the die cushion "up" force such that the primary cushion force will not follow the press ram "up" stroke.